The present invention relates to a turbidimeter which is preferably used for measuring the turbidity of a culture solution or suspension in a fermentation apparatus.
When measuring the turbidity of culture solutions in industrial apparatuses, a tungsten lamp is widely used as the light source. However, the tungsten lamp has many drawbacks such that its light intensity varies greatly, its life cycle is short, its temperature becomes high and the color of test solutions is greatly affected. In order to eliminate the drawbacks mentioned above, there has been proposed in, for example, Japanese Patent Publication No. 49,551/81 a turbidimeter using a light-emitting diode as the light source. However, since it is not possible to measure the turbidity above 10% due to the weak light emitted from the light-emitting diode and the measurement is largely affected by temperature, it is necessary to measure the test solution or a diluted test solution by introducing it into a flowcell manually or through a bypass pipe without directly immersing the turbidimeter in the test solution in the apparatus. Therefore, there occurs a drawback such that the apparatus is liable to be large in size and complicated in construction. Especially in the case of measuring a diluted test solution, the measuring accuracy is largely affected by errors due to the dilution.
Further, there is disclosed in "Applied Microbiology," vol 27, No. 5, May 1974, pages 874-877 and Japanese Utility Model Laid-Open Publication No. 201,954/83 a turbidimeter utilizing a He-Ne gas laser as the light source and a photomultiplier tube as a light-receiving device. in
In the turbidimeter mentioned above, since the He-Ne gas laser emits strong laser light, there is the possibility of measuring a test solution having relatively large turbidity without diluting it. However, since the He-Ne gas laser device and the apparatus including the photomultiplier tube are liable to be large in size, it is very difficult to install them integrally with the industrial apparatus together with a detection device. Therefore, it is necessary to arrange the He-Ne gas laser device and the apparatus including the photomultiplier tube separately from the industrial apparatus containing the test solution i.e. a suspension to be measured therein and to connect therebetween by means of optical fibers, so that the strong laser light cannot be utilized effectively due to a loss of laser light transmitting through the optical fibers or connectors of the optical fibers. Moreover, the apparatus becomes large in size and inspection and maintenance thereof become very troublesome.